Method and apparatus for extracting bitumen from an oil sand stream

ABSTRACT

The present invention provides a method for extracting bitumen from an oil sand stream, the method including the steps of: (a) providing an oil sand stream; (b) contacting the oil sand stream with a solvent thereby obtaining a first solvent-diluted oil sand slurry; (c) screening the first solvent-diluted oil sand slurry, thereby obtaining a first oversized material and a first undersized material; (d) contacting the first oversized material with a solvent thereby obtaining a second solvent-diluted oil sand slurry; (e) screening the second solvent-diluted oil sand slurry, thereby obtaining a second oversized material and a second undersized material; (f) optionally filtering the first undersized material obtained in step (c), thereby obtaining a solids-depleted stream and a solids-enriched stream; (g) optionally removing solvent from the solids-depleted stream obtained in step (f) thereby obtaining a bitumen-enriched stream.

RELATED APPLICATIONS

This application claims the benefit of US Provisional Application No.61/766,015 filed Feb. 18, 2013, which is incorporated herein byreference.

BACKGROUND

The present invention relates to a method for extracting bitumen from anoil sand stream.

Various methods have been proposed in the past for the recovery ofbitumen (sometimes referred to as “tar” or “bituminous material”) fromoil sands as found in various locations throughout the world and inparticular in Canada such as in the Athabasca district in Alberta and inthe United States such as in the Utah oil sands. Typically, oil sand(also known as “bituminous sand” or “tar sand”) comprises a mixture ofbitumen (in this context also known as “crude bitumen”, a semi-solidform of crude oil; also known as “extremely heavy crude oil”), sand,clay minerals and water. Usually, oil sand contains about 5 to 25 wt. %bitumen (as meant according to the present invention), about 1 to 13 wt.% water, the remainder being sand and clay particles.

As an example, it has been proposed and practiced at commercial scale torecover the bitumen content from the oil sand by mixing the oil sandwith water and separating the sand from the aqueous phase of the slurryformed.

Other methods have proposed non-aqueous extraction processes to reducethe need for large quantities of process water.

A problem of known methods of extraction of bitumen from oil sand is thehandling of oil sand ore, in particular the bitumen lumps being presenttherein. The breaking down of such bitumen lumps takes a lot of time andrequires long overall residence time and large equipment.

It is an object of the present invention to improve the handling of oilsand ore.

It is a further object of the present invention to provide a moreefficient handling of oil sand ore in an oil sand stream, in particularwhen bitumen is to be extracted from the oil sand stream using anon-aqueous solvent.

One or more of the above or other objects may be achieved according tothe present invention by providing a method for extracting bitumen froman oil sand stream, the method comprising at least the steps of:

-   -   (a) providing an oil sand stream;    -   (b) contacting the oil sand stream with a solvent thereby        obtaining a first solvent-diluted oil sand slurry;    -   (c) screening the first solvent-diluted oil sand slurry, thereby        obtaining a first oversized material and a first undersized        material;    -   (d) contacting the first oversized material with a solvent        thereby obtaining a second solvent-diluted oil sand slurry;    -   (e) screening the second solvent-diluted oil sand slurry,        thereby obtaining a second oversized material and a second        undersized material;    -   (f) optionally filtering the first undersized material obtained        in step (c), thereby obtaining a solids-depleted stream and a        solids-enriched stream;    -   (g) optionally removing solvent from the solids-depleted stream        obtained in step (f) thereby obtaining a bitumen-enriched        stream.

The method according to the present invention provides a surprisinglysimple and elegant manner to handle oil sands ore in an oil sand stream.It has surprisingly been found according to the present invention that alarge proportion of the bitumen lumps break down quickly and can passthe screen in step (c) after only a short contacting time in step (b).The remaining bitumen lumps are subjected to further mixing andscreening and, as the size of this stream has been significantlyreduced, smaller equipment can be used.

An important advantage of the present invention is that it allows areduction in overall size requirement, and, in some embodiments, inparticular where the contacting and screening steps are integrated inone device, a reduction in the number of rotary seals and a reduction inthe number of drive assemblies, when compared to performing the mixing,screening operations in separate devices.

A further advantage according to the present invention is that coarsesolids as present in the oil sand do not require to be transportedbetween separate devices for mixing, screening and drying/solventremoval. The handling of such coarse solids is already a challenge inconventional oil sand processes, but much more difficult in case anon-aqueous solvent (which typically comprises a volatile hydrocarbon)is to be used for extracting bitumen from the oil sand.

According to the present invention, the providing of the oil sand streamin step (a) can be done in various ways. Typically, oil sand is reducedin size, e.g. by crushing, breaking and/or grinding, to below a desiredsize upper limit Preferably, the oil sand provided in step (a) has aparticle size of less than 20 inch, preferably less than 16 inch, morepreferably less than 12 inch. Also, the oil sand stream provided in step(a) is typically subjected to a deoxygenation step; this is ofparticular relevance if the solvent as used in step (b) is a flammablesolvent.

In step (b), the oil sand is contacted with a solvent in the firstsection thereby obtaining a first solvent-diluted oil sand slurry. Theperson skilled in the art will understand that, in particular when thesolvent is recycled from a downstream point in the process, it maycontain some bitumen.

The solvent as used in the method of the present invention may beselected from a wide variety of solvents, including water, aromatichydrocarbon solvents and saturated or unsaturated aliphatic (i.e.non-aromatic) hydrocarbon solvents; aliphatic hydrocarbon solvents mayinclude linear, branched or cyclic alkanes and alkenes and mixturesthereof. Preferably, the solvent in step (b) comprises a non-aqueoussolvent. Preferably, the solvent in step (b) comprises an aliphatichydrocarbon having from 3 to 9 carbon atoms per molecule, morepreferably from 4 to 7 carbons per molecule, or a combination thereof.Especially suitable solvents are saturated aliphatic hydrocarbons suchas propane, butane, pentane, hexane, heptane, octane and nonane(including isomers thereof), in particular butane, pentane, hexane andheptane. It is preferred that the solvent in step (b) comprises at least90 wt. % of the aliphatic hydrocarbon having from 3 to 9 carbon atomsper molecule, preferably at least 95 wt. %. Also, it is preferred thatin step (b) substantially no aromatic solvent (such as toluene orbenzene) is present, i.e. less than 5 wt. %, preferably less than 1 wt.%. Further it is preferred that a single solvent is used as this avoidsthe need for a distillation unit or the like to separate solvents. Also,it is preferred that the solvent has a boiling point lower than that ofthe bitumen to facilitate easy separation and recovery.

Furthermore, if desired, additional process fluids may be added, such aswater and/or agglomeration agents, for example to aid in achievingdesired slurry properties through agglomeration of fine particles.

In step (c), the first solvent-diluted oil sand slurry is screened,thereby obtaining a first oversized material and a first undersizedmaterial. Typically, the first solvent-diluted oil sand slurry screenedor reduced in size to have a diameter below 5.0 cm, preferably below 2.0cm, more preferably below 1.0 cm. If the screening is performed in thepresence of non-aqueous solvent, this helps breaking down the larger(bitumen-containing) lumps and dissolving the bitumen.

In step (d), the first oversized material is contacted with a solventthereby obtaining a second solvent-diluted oil sand slurry. Preferably,the solvent in step (d) comprises a non-aqueous solvent. It is even morepreferred that the solvent as used in steps (b) and (d) is the same.

In step (e), the second solvent-diluted oil sand slurry is screened,thereby obtaining a second oversized material and a second undersizedmaterial. If desired, solvent may be removed from the second oversizedmaterial thereby obtaining solvent-depleted oversized material (the“rejects”). Although the removal of solvent may be performed in variousways, it usually includes heating and preferably the use of a purge gas,such as N₂ or steam. The second undersized material may be processedseparately and e.g. sent to a filter, but is typically combined with thefirst undersized material as mentioned below.

In optional step (f), the first undersized material obtained in step (c)is filtered, thereby obtaining a solids-depleted stream and asolids-enriched stream. This filtration step is not limited in any way.As the person skilled in the art is familiar with how to perform such afiltration step, this is not further discussed here in detail. Accordingto an especially preferred embodiment, the first undersized materialobtained in step (c) is combined with the second undersized materialobtained in step (e), before being filtered in step (f).

In optional step (g), solvent is removed from the solids-depleted streamobtained in step (f) thereby obtaining a bitumen-enriched stream. Thisbitumen-enriched stream may be sent to a refinery or the like forfurther processing. As the person skilled in the art is familiar withhow to remove the solvent and process the bitumen-enriched stream, thisis not further discussed here in detail.

In a further aspect the present invention provides a an apparatus forperforming the method according to the present invention, at leastcomprising:

-   -   a housing containing a first section, a second section, a third        section and a fourth section;    -   the first section having a first inlet for oil sand, a second        inlet for a solvent and an outlet for a first solvent-diluted        oil sand slurry;    -   the second section having an inlet for the first solvent-diluted        oil sand slurry, a screen allowing a first undersized material        to pass and an outlet for a first oversized material; and    -   the third section having a first inlet for the first oversized        material, a second inlet for a solvent and an outlet for a        second solvent-diluted oil sand slurry;    -   the fourth section having an inlet for the second        solvent-diluted oil sand slurry, a screen allowing a second        undersized material to pass and an outlet for a second oversized        material;

wherein the first section, the second section, the third section and thefourth section can rotate (as a single rotating device) during usearound a common rotation axis.

An advantage of the apparatus according to the present invention is thatthe oil sand stream can be handled in a surprisingly simple and elegantmanner by providing a two-stage mixing and screening operation in asingle rotating drum.

The housing and first, second, third and fourth sections as used in theapparatus according to the present invention are not limited in any way.There may be more sections present than the first, second, third andfourth sections (thereby creating further contacting and screeningareas). The housing typically surrounds the first, second, third andfourth (and optional further) sections and ensures that no undesiredleakage of vapours to the environment occurs; this is of particularrelevance if a non-aqueous solvent is used in the first and/or thirdsections. The housing may be formed by the outer walls of the first,second, third and fourth sections and hence does not need to be aseparate element. The housing does not necessarily (but preferably will)co-rotate during use with the first, second, third and fourth sections.Preferably, the first inlet of the first section, the inlet of thesecond section, the first inlet of the third section and the inlet ofthe fourth section are axial inlets; also it is preferred that theoutlet of the first section, the outlet of the second section, theoutlet of the third section and the outlet of the fourth section areaxial outlets. It goes without saying that further inlets and outletsmay be present (which may be axial or not).

The screens of the second and fourth (and any further) sections may bepartly integrated with the housing of the respective sections, forexample through a discharge grate which may form part of the (typicallyvertical) wall near the outlet of the respective section. As dischargegrates are known in the art, these are not further discussed here.

During use of the apparatus according to the present invention, in thefirst section, oil sand is contacted with solvent, preferably anon-aqueous solvent (and typically, if the solvent is recycled from adownstream point of the process with some dissolved bitumen as well)thereby obtaining a first solvent-diluted oil sand slurry. In the secondsection, the first solvent-diluted oil sand slurry is screened to allowa first undersized material to pass; a first oversized material istransferred to the third section. In the third section the firstoversized material is contacted with solvent thereby obtaining a secondsolvent-diluted oil sand slurry. The second solvent-diluted oil sandslurry is transferred to the fourth section and screened therein,thereby obtaining a second oversized material and a second undersizedmaterial. Whilst the oil sand is passing through the first, second,third and fourth sections, these sections rotate around a commonrotation axis (i.e. as a single rotating drum).

Solvent is typically removed from the second oversized material therebyobtaining solvent-depleted oversized material; this solvent-depletedoversized material (“rejects”) is typically discharged for disposalafter the solvent has been removed. Care is taken that substantially nosolvent vapour escapes from the contained processing environment in thehousing and hence also no solvent vapour escapes with thesolvent-depleted oversized material.

The first and second undersized materials are typically furtherprocessed. Preferably, the first and second undersized materials aresent to a filter as mentioned above.

The first section, the second section, the third section and the fourthsection can rotate during use around a common rotation axis. Typically,the first, second, third and fourth sections (and preferably the housingas well) can co-rotate around the common rotation axis as one singlerotation assembly (i.e. in the same direction and at the same speed).

The progression of the oil sand, slurry and other solids containingstreams through the apparatus may be aided by inclining the first,second, third and fourth sections a few degrees from horizontal (whereinthe first section is at a higher point than the second section, thesecond section at a higher point than the third section and the thirdsection at a higher point than the fourth section), e.g. as done in acalcining kiln. In addition or alternatively, lifters and/or flutes maybe placed in such a way to mechanically aid the progression of the solidcontaining streams or retain it in one area for a longer time. The useof lifters also aids in the agitation and contact of bitumen and solventin the first section and hence accelerates the bitumen dissolutionprocess, although agitation should not be so great as to break upsignificant clay lumps which can hinder downstream processing. Balls orrods may be present in the first section and/or third section to promotethe disintegration of relatively big bitumen-containing lumps.

Preferably, the screen of the second section and the housing define anannular pathway arranged around the screen for removing the firstundersized material passed through the screen. As mentioned above, thehousing may be formed by the outer walls of the first, second, third andfourth sections and does not need to be a separate element. In the casewherein the screen of the second section and the housing define anannular pathway arranged around the screen, the outer wall of the secondsection and the housing may coincide. Preferably, the annular pathway atleast partially surrounds the third section; in this case the wall ofthe housing does not coincide with the wall of the third section but isa separate element.

It is also preferred that—similar to the screen of the secondsection—the screen of the fourth section and the housing define anannular pathway arranged around the screen for removing the secondundersized material passed through the screen. Preferably, both anannular pathway around the screen of the second section and around thescreen of the fourth section are present, both pathways being connected,preferably aligned.

Further it is preferred that the annular pathway (either around thescreen of the second section, around the screen of the fourth section orboth) is fluidly connected to an inlet of a filtration unit. Preferably,the undersized material removed via the annular pathway is thickened(i.e. made denser) prior to feeding to the filtration unit. To that end,the apparatus preferably comprises a thickener between the annularpathway and the inlet of the filtration unit, typically in the form of ahydrocyclone or the like.

Preferably, the apparatus comprises a threshold between the firstsection and second section. Similarly, it is preferred that theapparatus comprises a threshold between the third section and fourthsection. Such threshold(s) may be created in various manners and allowthat the residence time in the first and third section(s) is increased.One example of such a threshold would be the use of an inward facingring between the respective sections. Preferably a threshold is createdby having a reduced diameter for the second (and/or fourth) section(where screening takes place) relative to the preceding first (and/orthird section). The person skilled in the art will readily understandthat further thresholds may be present in case the apparatus comprisesfurther sections for contacting and screening; in such case thethreshold(s) is (are) preferably located at the inlet of a furtherscreening section.

According to a preferred embodiment of the apparatus according to thepresent invention, the apparatus comprises an inner screen which isconcentrically arranged with respect to the screen of the second sectionand the screen of the fourth section. In the second section and thefourth section the inner screen is surrounded (at a predetermineddistance) by the respective screens. Such an inner screen helps to keepthe larger rocks away from the more fragile screens of the second andfourth section, respectively. Preferably, the inner screen connects theoutlet of the first section to the outlet of the fourth section; in thelatter case, the inner screen runs through the second, third and fourthsection. In case the apparatus comprises more than two screeningsections (such as the second and fourth sections), the inner screen maybe surrounded by the screen of such further screening sections.

The apparatus may comprise one or more outlets for solvent vapour. Theoutlet for solvent vapour may be located at various places (such as inany of the first to fourth section), but is preferably located in thefourth section. Preferably, the outlet for solvent vapour is connectedto an inlet of a solvent recovery unit. Furthermore, the apparatusaccording to the present invention typically comprises an inlet for apurge gas, such as N₂ or steam. Preferably, the outlet for solventvapour as mentioned above also functions as an outlet for the purge gas.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter the invention will be further illustrated by the followingnon-limiting drawings. Herein shows:

FIG. 1 schematically a first non-limiting embodiment of an apparatus inaccordance with the present invention; FIG. 2 a cross-section throughthe apparatus of FIG. 1 at line B-B′ to illustrate the annular pathway7A;

FIGS. 3-6 schematically a part of further non-limiting embodiments of anapparatus in accordance with the present invention; and

FIG. 7 a cross-section through the apparatus of FIG. 6 at line C-C′ toillustrate the relative position of the annular inner screen 23.

DETAILED DESCRIPTION OF THE DRAWINGS

For the purpose of this description, a single reference number will beassigned to a line as well as a stream carried in that line.

FIG. 1 schematically shows a simplified apparatus according to thepresent invention for removing rejects from an oil sand stream, fromwhich subsequently bitumen is to be extracted. The apparatus isgenerally referred to with reference numeral 1. The apparatus 1comprises a cylindrical housing 2 that rotates during use around theaxis A-A′. Housing 2 comprises a first section 3 (formixing/contacting), a second section 4 (for screening), a third section5 (for mixing/contacting) and a fourth section 6 (for screening)contained therein. Further shown is a filtration unit 8, a VRU (vapourrecovery unit) 9, a solvent source 11, a deoxygenator 12, rotating seals13, a pumpbox 14, a conveyor belt 15, a clarifier 16, a drier 17 and ahydrocyclone 18.

The first section 3 has a first (axial) inlet 31 for oil sand, a secondinlet 32 for solvent (which may feed into the second, third and fourthsections as well) and an (axial) outlet 33 for a first solvent-dilutedoil sand slurry. Also, the first section 3 has tapering guide plates 34for guiding the solvent-diluted oil sand slurry towards the (axial)outlet 33/inlet 41.

The second section 4 has an (axial) inlet 41 for the firstsolvent-diluted oil sand slurry (which inlet 41 corresponds to theoutlet 33 of the first section 3), a(n annular) screen 42 allowing afirst undersized material to pass and an (axial) outlet 43 for a firstoversized material.

The third section 5 has a first (axial) inlet 51 for the first oversizedmaterial (which first inlet 51 corresponds to the outlet 43 of thesecond section 4), a second inlet 52 for a solvent and an (axial) outlet53 for a second solvent-depleted oil sand slurry.

The fourth section 6 has an (axial) inlet 61 for the secondsolvent-diluted oil sand slurry, a(n annular) screen 62 allowing asecond undersized material to pass and an outlet 63 for a secondoversized material. Also, the fourth section 6 has an inlet 64 for apurge gas, such as N₂ or steam. The purge gas inlet 64 may also belocated in one of the other sections; also, there may be two or more ofsuch purge inlets. The fourth section 6 may further comprise an outlet65 for solvent vapour and/or purge gas. In the embodiment of FIG. 1,outlet 65 is connected to an inlet of a solvent recovery unit 9.

In the embodiment of FIG. 1, the screen 42 of the second section 4 andthe housing 2 (which in the embodiment of FIG. 1 coincides with theouter wall of the second section 4) define an annular pathway 7Aarranged around the screen 42 (and in the embodiment of FIG. 1 alsoaround third section 5) for removing the first undersized materialpassed through the screen 42. Similarly, the screen 62 of the fourthsection 6 and the housing 2 define an annular pathway 7B arranged aroundthe screen 62 for removing the second undersized material passed throughthe screen 62. The annular pathways 7A and 7B are connected and (in theembodiment of FIG. 1) aligned. The annular pathways 7A and 7B arefluidly connected to the inlet 81 of the filtration unit 8, via thepumpbox 14 and the hydrocyclone 18.

The first section 3, the second section 4, the third section 5 and thefourth section 6 can co-rotate during use as one single rotationassembly (preferably also including the housing 2) around the commonrotation axis A-A′. Typically, the axis A-A′ is at a slight angle (up to3°) with the horizontal to assist the (slightly downwards) flow from thefirst section 3 into the second section 4 and then into the thirdsection 5 and fourth section 6. For the sake of simplicity no driver hasbeen shown for achieving the rotation of the first section 3, the secondsection 4, the third section 5 and the fourth section 6; the personskilled in the art will readily understand that this driver is notlimited in any way. Preferably, (and as shown in FIGS. 3-5) there arethresholds (e.g. by using reduced diameters for the second and fourthsections) between the first section 3 and second section 4 and betweenthe third section 5 and fourth section 6 to increase the residence timein the first section 3 and the third section 5 for enhanced mixing.

As shown in the embodiment of FIG. 1, the housing 2 is preceded by adeoxygenation unit 12.

During use of the apparatus 1 as embodied in FIG. 1, a crushed oil sandstream 10 is sent to a de-oxygenation unit 12 to remove oxygen.Subsequently, the deoxygenated oil sand is passed as stream 20 to andfed into the first section 3 (for mixing) for contacting the oil sandstream with a solvent such as pentane thereby obtaining a firstsolvent-diluted oil sand slurry. The solvent may be obtained as stream80 from solvent source 11 (fed via inlet 32), and/or recycled from apoint downstream in the process (e.g. stream 100; although in FIG. 1,stream 100 is fed just upstream of the first section 3). Balls or rodsmay be added to the first section 3 (and/or third section 5) to promotethe disintegration of relatively big bitumen-containing lumps.

The first solvent-diluted oil sand slurry is screened in the secondsection 4 (for screening) using the screen 42, thereby obtaining a firstoversized material and a first undersized material. The first oversizedmaterial is passed to the third section 5 (for mixing) to be contactedwith solvent (fed via inlet 52), thereby obtaining a secondsolvent-diluted oil sand slurry. The second solvent-diluted oil sandslurry is screened in fourth section 6 (for screening), therebyobtaining a second oversized material and a second undersized material.

The second oversized material (or “rejects”) 70 is removed via e.g. aconveyor belt 15 (alternatively, lifters or the like may be used insteadof a conveyor belt). The rejects 70 can be used e.g. for landreclamation or simply disposed, possibly after further solvent removal.

The first undersized material as obtained in the second section 4 andthe second undersized material as obtained in the fourth section 6 flowthrough the annular pathway 7A defined by the screen 42 and the housing2 and the pathway 7B as defined by the screen 62 and the housing 2 tothe pumpbox 14. Then, it is pumped as stream 30 to hydrocyclone 18 forthickening. The thickened undersized material is subsequently sent asstream 35 to the inlet 81 of the filtration unit 8 and filtered therebyobtaining a solids-depleted stream 40 and a solids-enriched stream 50(if desired, using solvent stream 90 from the solvent source 11).Solvent is removed from the solids-enriched stream 50 in drier 17thereby obtaining a dried solids-enriched stream 60 which is oftenreferred to as “tailings”. The solids-depleted stream 40 is relativelybitumen-rich and is further processed (as stream 40A) to recover thebitumen which may be further upgraded in a refinery (not shown) or thelike; usually, the solids-depleted stream 40A is first sent to aclarifier 16. As shown in FIG. 1 part 40B of the solids-depleted stream40 may be reused in the process, e.g. as solvent to be used for thecontacting in the first section 3 and/or third section 5. Also,solids-depleted stream 100 recovered from stream 30 in hydrocyclone 18may be combined with the deoxygenated oil sand stream 20.

FIG. 2 shows a cross-section through the apparatus 1 of FIG. 1 at lineB-B′ (through second section 4) to further illustrate the annularpathway 7A defined by the screen 42 and the housing 2 (coinciding withthe outer wall of the second section 4).

FIGS. 3-6 schematically show a part of further non-limiting embodimentsof an apparatus 1 in accordance with the present invention. Not alllines and components have been shown in FIGS. 3-6. The embodiments ofFIGS. 3-6 all have thresholds between the first section 3 and secondsection 4 and between the third section 5 and fourth section 6 (andbetween the fifth section 21 and sixth section 22) to increase theresidence time in the first section 3 and the third section 5 (and fifthsection 21) for enhanced mixing. The threshold is created by a reduceddiameter for the second section 4 and fourth section 6 (and sixthsection 22), when compared with the diameter for the first section 3 andthird section 5 (and fifth section 21), respectively.

Further, FIGS. 3-4 show that the undersized material from the screens ofsections 4 and 6 may be removed in other ways than through the annularpathway 7A,7B as shown in FIG. 1.

In the embodiment of FIG. 5, the apparatus comprises a fifth section 21and sixth section 22; hence, the embodiment of FIG. 5 has 3 stages ofcontacting/mixing and screening. The screen 25 of the sixth section 6and the housing 2 define an annular pathway 7C arranged around thescreen 25 for removing the second undersized material passed through thescreen 25. Annular pathway 7C is aligned with annular pathways 7A and7B.

In the embodiment of FIG. 6 (again comprising a fifth section 21 and asixth section 22), an additional (annular) inner screen 23 is included.The inner screen 23 connects the outlet 33 of the first section 3 to(the outlet 63 of the fourth section 6 and) the outlet 24 of the sixthsection 22 and hence passes through second section 4, third section 5,fourth section 6, fifth section 21 and sixth section 22. The innerscreen 23 is relatively ‘coarse’, i.e. allows more material to pass thanthe screens 42,62,25 do. Such an inner screen 23 helps to keep thelarger rocks away from the more fragile screens 42,62,25.

FIG. 7 shows a cross-section through the apparatus 1 of FIG. 6 at lineC-C′ (through second section 4) to further illustrate the annularpathway 7A defined by the screen 42 and the housing 2, and the relativeposition of the (annular) inner screen 23 with respect to the screen 42.As can be seen in FIG. 7, the inner screen is concentrically arrangedwith respect to screen 42 of the second section 4 (and similarly withrespect to screen 62 of the fourth section 6 and screen 25 of the sixthsection 22).

The person skilled in the art will readily understand that manymodifications may be made without departing from the scope of theinvention. Further, the person skilled in the art will readilyunderstand that, while the present invention in some instances may havebeen illustrated making reference to a specific combination of featuresand measures, many of those features and measures are functionallyindependent from other features and measures given in the respectiveembodiment(s) such that they can be equally or similarly appliedindependently in other embodiments.

What is claimed is:
 1. A method for extracting bitumen from an oil sandstream, the method comprising at least the steps of: (a) providing anoil sand stream; (b) contacting the oil sand stream with a solventthereby obtaining a first solvent-diluted oil sand slurry; (c) screeningthe first solvent-diluted oil sand slurry, thereby obtaining a firstoversized material and a first undersized material; (d) contacting thefirst oversized material with a solvent thereby obtaining a secondsolvent-diluted oil sand slurry; (e) screening the secondsolvent-diluted oil sand slurry, thereby obtaining a second oversizedmaterial and a second undersized material; (f) optionally filtering thefirst undersized material obtained in step (c), thereby obtaining asolids-depleted stream and a solids-enriched stream; (g) optionallyremoving solvent from the solids-depleted stream obtained in step (f)thereby obtaining a bitumen-enriched stream.
 2. The method according toclaim 1, wherein the solvent in step (b) comprises a non-aqueoussolvent.
 3. The method according to claim 1, wherein the solvent in step(d) comprises a non-aqueous solvent.
 4. The method according to claim 1,wherein the first undersized material obtained in step (c) is combinedwith the second undersized material obtained in step (e), before beingfiltered in step (f).
 5. An apparatus for performing the methodaccording to claim 1, at least comprising: a housing containing a firstsection, a second section, a third section and a fourth section; thefirst section having a first inlet for oil sand, a second inlet for asolvent and an outlet for a first solvent-diluted oil sand slurry; thesecond section having an inlet for the first solvent-diluted oil sandslurry, a screen allowing a first undersized material to pass and anoutlet for a first oversized material; and the third section having afirst inlet for the first oversized material, a second inlet for asolvent and an outlet for a second solvent-diluted oil sand slurry; thefourth section having an inlet for the second solvent-diluted oil sandslurry, a screen allowing a second undersized material to pass and anoutlet for a second oversized material; wherein the first section, thesecond section, the third section and the fourth section can rotateduring use around a common rotation axis (A-A′).
 6. The apparatusaccording to claim 5, wherein the screen of the second section and thehousing define an annular pathway arranged around the screen forremoving the first undersized material passed through the screen.
 7. Theapparatus according to claim 5, wherein the screen of the fourth sectionand the housing define an annular pathway arranged around the screen forremoving the second undersized material passed through the screen. 8.The apparatus according to claim 6, wherein the annular pathway isfluidly connected to an inlet of a filtration unit.
 9. The apparatusaccording to claim 5, comprising a threshold between the first sectionand second section.
 10. The apparatus according to claim 5, comprising athreshold between the third section and fourth section.
 11. Theapparatus according to claim 5, comprising an inner screen which isconcentrically arranged with respect to the screen of the second sectionand the screen of the fourth section.
 12. The apparatus according toclaim 11, wherein the inner screen connects the outlet of the firstsection to the outlet of the fourth section.